Advanced laser crystallization of Si films for large flat panel displays requires a narrow very homogeneous focus with at
least 235 mm length and high depth of focus. Earlier we have reported on the development and application of an ultranarrow
(5-9 μm) homogeneous line-shaped laser focus of 60 mm length for sequential lateral solidification (SLS) of Si.
Key element of our line shaping system is an anisotropic mode transformation of the 2nd green harmonic of a Nd:YAG
laser beam and its following homogenization for the long focus axis. The design and built-up of a much longer "green
line" requires innovative optical approaches and very high precision optical manufacturing. We analyze in detail
different process requirements, their physical compatibility (e.g. line width vs. depth of focus) and practical feasibility.
To reach high energy densities in the long lines we design optical schemas bundling up to 8 beams of separate lasers.

Many laser applications need a homogeneous - so called flat hat - light distribution in the application area. However,
many laser emit Gaussian shaped light. The technology of diffractive optical elements (DOE) can be used to shape the
Gaussian beam into a flat hat beam at a compact length. SCHOTT presents a DOE design of a flat hat DOE beam shaper
made out of optical glass. Here the material glass has the significant advantage of high laser durability, low scattering
losses, high resistance to temperature, moisture, and chemicals compared to polymer DOEs. Simulations and
measurements on different DOEs for different wavelength, laser beam width, and laser divergence are presented.
Surprisingly the flat hat DOE beam shaper depends only weakly on wavelength and beam width but strongly on laser
divergence. Based on the good agreement between simulation and measurement an improved flat hat DOE beam shaper
is also presented.

Fly's eye condensers are commonly used for the beam shaping of an arbitrary input intensity distribution into a
top hat. The setup usually consists of a Fourier lens and two identical regular microlens arrays - often referred
to as tandem lens array - where the second one is placed in the focal plane of the first microlenses. The output
intensity distribution is modulated by equidistantly located sharp intensity peaks due to the periodic structure
of the regular arrays. In a chirped array, the inflexibility of a regular structure has been overcome. Hence, an
array can be formed which is non-periodic and consequently the equidistantly located intensity peaks can be
suppressed. A far field speckle pattern results with more densely and irregularly located intensity peaks leading
to an improved homogeneity of the intensity distribution. Additionally, a stochastic array which features a nonperiodic
layout can be used in order to avoid the equidistantly located intensity peaks. Again, a far field speckle
pattern results with more densely and irregularly located intensity peaks leading to an improved homogeneity
of the intensity distribution. We compare fly's eye condensers based on regular, chirped and stochastic tandem
microlens arrays in terms of achievable intensity homogenization, design and fabrication methods and their
advantages and disadvantages in their applications.

Shaping laser beams within the laser cavity can improve the laser power efficiency and allows the generation of
predetermined beam structures suitable for various applications such as metrology, lithography and particle
manipulation. In this work we study a resonator in which one of the mirrors is replaced by a conical reflector and derive
resonator parameters for required beam selections. For example, we show that choosing a negative cone angle can lead to
oscillation on pure high-order modes corresponding to the first and second order Bessel functions in the resonator
integral equation kernels. These modes possess a distinct zero intensity on the axis that can be exploited for applications
such as singular beam metrology and particle manipulation. To generate the specific beam structures we found optimal cone angles and mirror sizes for stable resonators with two configurations, close to flat and to concentric. These optimal conditions were derived by requiring that the selected mode has minimal diffraction loss. It is shown that the selection of these higher-order modes is more efficient in the concentric configuration.

A new type of electro-optical (E-O) deflector which combines microoptical laser beam manipulations and electro-optical
light wave phase control is presented. It consists of two stages, which include E-O arrays of LiNbO3 as key components.
The first stage forms a moveable "comb" of interference beamlets at the entrance to the second one. The second stage
recombines the beamlets, reconstructs a plane wavefront and converts the translational movement of the comb to an
angular deflection of the unified beam. Advantages of the concept as compared to other deflector types will be discussed.
The laboratory results with He-Ne lasers are presented. The demonstrator is designed to provide a 63 mrad deflection
with a diffraction limited resolution of 0.025 mrad. The technique is applicable for material processing with highrepetition-
rate lasers, for laser projection, lidars and in other fields where high speeds and robustness are necessary or
sources of vibration need to be avoided.

The different propagating modes in an optical fiber determine the properties of the light emerging the fiber.
Therefore an exact knowledge of the modal content is a key to understand the underlying physical effects. Different
approaches exist to measure the modal content of an optical fiber, such as interferometry, M2 measurement
or phase retrieval methods with either high experimental complexity or ambiguity relating to the modal content.
In this paper we present a method for measuring the modal content by the aid of optical correlation analysis.
We demonstrate this with measurements on a passive step-index LMA fiber at a wavelength of 1064 nm.

Direct laser patterning of various materials is today widely used in several micro-system production lines like inkjet
printing, solar cell technology, flat-panel display production and medicine. Typically single-mode solid state lasers and
their higher harmonics are used especially for machining of holes and grooves. The most prominent lasers are pulsed
Nd:YAG lasers and their harmonics @ 266, 355 and 532 nm. Recently, the striking advantages of flat top intensity
distributions for the efficiency and quality of these processes were demonstrated. The use of LIMO's compact Gaussian-to-
top-hat converter enables the creation of steeper and sharper edges. Additionally, the higher energy efficiency of
rectangular top hat profiles compared to smooth, circular Gaussian shapes allows for faster patterning. A standard
method to reduce process times is the use of optical scanning systems. Yet, the application of Gaussian-to-top-hat
converters in combination with a scanner was hindered by distortions of the top hat introduced by the F-Theta focussing
lens of the scanners even at very small deflection angles (<2°). We solved this challenge by implementing an alternative
scanning approach (patent pending). Scanning results obtained with a 50x50μm2 top hat field (homogeneity down to
<10%) in a scan area of 156x156mm2 will be presented. The minimal distortions of the top hat observed within the scan
area make LIMO's compact Gaussian-to-top-hat converter excellently suited for industrial scanning applications, e.g. for
the processing of solar panels.

The problem of wavefront measurements is one of the most important tasks in the modern optics and laser physics. There
are lots of different tools for wavefront measurement. And the user might choose any type of instrument which could
solve certain task. The devices for wavefront analysis differ from each other not only by setup and by processing
algorithms but also dynamic range and accuracy should be taken into account. The most popular devices are Shack-
Hartmann wavefront sensor and various types of interferometers.
In this paper we compare Shack-Hartmann wavefront sensor with Fizeau interferometer; classical analysis of
interferograms (based on measurement of the fringe centers position) and phase-shifting methods are also compared.
Advantages and disadvantages of three methods are discussed.

Modal decomposition by means of correlation filters has been proved as a key for real online laser beam analysis.
To compare that method with the "standard" M2 method, we generated series of different laser beams (1064 nm),
applied both methods to one and the same beam and evaluated achieved results. An adjustable Nd:YAG laser
served as transversal mode generator, delivering diverse "pure" Gauss-Hermite modes and superpositions of
modes, respectively. In the case of incoherent superposition of modes, their particular contribution to the
general M2 value should be proportional to their relative strength, whereas in the case of coherent superposition
M2 is distinctly influenced by phase differences between the discrete modal components. Achieved experimental
findings are well confirmed by computer simulation.

We experimentally demonstrate a compact self-aligned external cavity 25W high power laser diode bar at 976 nm
tunable over 0.5 nm with a bandwidth of 0.25 nm. The external cavity is based on double diffraction from a glass
reflective volume holographic grating (VHG). The wavelength tuning is performed by rotation of the VHG. Passive
alignment and fine wavelength tuning of the proposed external cavity are attractive new features over the state-of-the-art
active alignment method and fixed wavelength limitation currently used in wavelength stabilized high power laser diode
bars.

Multiple tunable laser lines were obtained by pumping solution of Rh6G in ethanol (1mM) by five pairs of the
second harmonic of a passively Q. switched and mode locked Nd:YAG laser. The time delays among the excitation
pulses were varied within coherence length of 1cm. Twenty one equally spaced lines were obtained by pumping dye
solution with ten pairs of excitation beams derived from the same source. It was possible to tune the wavelengths by
a microcontroller based mirror mounted stage. Number of lasing lines varied from minimum five to maximum
twenty one. The wavelength of output lines varied from 540 to 590nm. The pulse lengths were measured, using
Hadland Streak Camera, to vary from minimum 10 to maximum 30ps. The experimental results have lead to
maturity of a 21-lines model of a distributed feedback dye laser. The dye cell was excited by the 2nd harmonic of a
laboratory built passively Q. switched and mode-locked Nd:YAG laser to induce simultaneous temperature phase
grating in the dye solution. This work on distributed feedback dye laser is in agreement with most of the published
results on semiconductor DFB lasers. Simultaneous operation of 21-lines of slightly varying wavelengths opens a
new era of research in biosensors, multiphoton ignition and measurements. This multi-wavelength operation of
DFDL is based on mutual couplings of five overwritten dynamic gratings.

Wavelength around 940 nm lasing can be obtained by quasi-three-level operation of Nd doped laser crystal.
Diode end pumping provides the necessary high pump intensity in the laser crystal. In order to get high efficiency of the
end pumped laser system, the overlap coefficient between pump beam and laser beam should be optimized. Thermal lens
coefficient is one of the most important parameters to design the laser cavity structure. The time dependent heat
conduction equation is solved numerically in order to study the thermal lens effect in pulsed pumping laser crystal.
Calculated results showed that the thermal lens coefficients change with different pump frequencies. Experiments are
done with Nd:YAG and Nd:GSAG laser rod. The thermal lens coefficient of Nd:YAG at pump frequency 50 Hz with
pump beam diameter 1.5 mm is 10.2 Wm, while the thermal lens coefficient of Nd:GSAG at pump frequency 50 Hz with
pump beam diameter 1.75 mm is 5.9 Wm.

The goal of this study is to demonstrate how a planar ensemble of Gaussian beams (TEM00) can be
modeled to create flattop beams for laser applications. We employed the Gaussian Beam Propagation
Method (GBPM) in the ASAP (BRO, Tucson AZ) computing and visualization environment in this
endeavor. Our study revealed that ensemble individual beam's widths must be set at 1.6 mm, half-angle
divergence cannot exceed .5 degrees. In addition, individual laser positions in the ensemble must be such
that all ensemble Gaussian beams reach the target/detector in phase. Such beam manipulations are critical
for many applications as they strive to customize industry de facto Gaussian laser beams into flattops. In
addition, our study has demonstrated that beam flatness is achievable without the aid of dissipative optical
entities.

The complex physical optics behavior in modern solid state lasers can only approximately be described using
common simulation techniques, such as a Gaussian mode analysis or beam propagation methods. For this reason
we present a new 3-dimensional, time-dependent method to model the laser beam in a resonator in a more
comprehensive way. We transform the wave equation by a special ansatz and solve the resulting equation, which
is similar to a Schroedinger equation, by a finite element analysis. In this paper we explain our new approach
and present first numerical results for a simple laser cavity. The results are compared with those of a dynamic
multimode analysis using Gaussian eigenmodes.

An actively Q-switched Nd:GSAG laser with 942nm wavelength was frequency doubled in a critically type-I
phase-matched LBO. Maximum pulse energy of 8mJ with 300ns pulse duration at 471 nm was obtained with 19mJ
incident radiation at 10Hz. The corresponding conversion efficiency was 42%. The frequency doubling of a focused
Gaussian beam involves spatially dependent phase mismatching due to beam divergence. It decreases the conversion
efficiency and deteriorates the beam quality. According to the theoretical calculation, elliptical focusing was used to
improve the second harmonic beam quality and slightly increase the conversion efficiency.

We show that the stimulated Raman process impairs multiple applications of ultra high Q whispering gallery
mode resonators and discuss possible ways of its suppression. One of the most promising ways is the coating of
the resonators with films containing spectrally selective absorbers able to reduce optical quality factor at Raman
Stokes frequencies and to leave without changes the quality factor of the modes of interest.

An optical waveguide consisting of coupled identical resonators in a linear array can slow down the propagation
of light and act as a delay line. However, such a slow-wave structure offers only a modest improvement in delay
per unit length over a spool of optical fiber, as its performance rapidly degrades if the resonators or their spacing
are not exactly identical. Here we show that the same degree of functionality can be achieved in a more compact
and disorder-immune structure, formed by nesting one resonator inside another, and thereby folding the light
path back onto itself.

We present the theory of operation along with detailed device designs and initial experimental results of a new class of
uncooled thermal detectors. The detectors, termed microphotonic thermal detectors, are based on the thermo-optic effect
in high quality factor (Q) micrometer-scale optical resonators. Microphotonic thermal detectors do not suffer from
Johnson noise, do not require metallic connections to the sensing element, do not suffer from charge trapping effects,
and have responsivities orders of magnitude larger than microbolometer-based thermal detectors. For these reasons,
microphotonic thermal detectors have the potential to reach thermal phonon noise limited performance.

Strong coupling between whispering gallery modes (WGMs) is studied in polystyrene bispheres by using spatially
resolved spectroscopy. The supermonodispersive pairs of spheres (size deviation <0.03%) were selected using their
uncoupled WGM peaks' positions. By using novel geometries of capturing light by the imaging spectrometer we
observed clear spectral signatures of strong coupling between WGMs for bispheres with mean sizes from 2.9 to 10 μm.
In a special geometry with the collection of light along the axis of bisphere and with the slit of the spectrometer oriented
perpendicular to the substrate we observed unusual and characteristic kites in the spectral images of such photonic
molecules. We showed that such kites allow unambiguous relating of the split components (antibonding and bonding
modes) in the spectral image to their WGM eigenstates in the uncoupled cavities. In many cases such kites simplify the
interpretation of the dense spectral images of bispheres. Using various geometries of the experiments we quantified the
dependence of coupling constant on the sizes of spheres for maximally coupled fundamental modes located in the
equatorial planes of spheres on the substrate. The results show the feasibility of achieving a coherent WGM-based
optical transport in microsphere resonator circuits.

Using the equilibrium configuration of an imprinted cholesteric elastomer film with a twist defect, we have found the
solution of the boundary value problem for the reflection and transmission of normal incident circularly polarized light
for different values of chiral order parameter. We have found resonant modes for both polarizations in smaller values of
chiral order parameter and in parameters related with elastic energy.

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Advanced PhotonicsJournal of Applied Remote SensingJournal of Astronomical Telescopes Instruments and SystemsJournal of Biomedical OpticsJournal of Electronic ImagingJournal of Medical ImagingJournal of Micro/Nanolithography, MEMS, and MOEMSJournal of NanophotonicsJournal of Photonics for EnergyNeurophotonicsOptical EngineeringSPIE Reviews